The applicants for the present application have previously developed an automated attendance tracking system. That system is disclosed in U.S. patent application Ser. No. 10/919,723, filed Aug. 16, 2004, published on Feb. 16, 2006 as Publication No. 2006/0035205, and the disclosure of that application is incorporated herein by reference in its entirety.
Generally, this and other Radio Frequency Identification (“RFID”) systems have an RFID transceiver antenna which emits electromagnetic radiation, typically with a frequency/wavelength corresponding with radio waves. This radiation is referred to as an RF signal and produces an RF field. The intensity of radiation in this field varies depending on where in the field the intensity is measured, with the field generally decreasing in intensity the further it is measured from the antenna linearly along a center line aligned with a direction the antenna is pointing. The intensity of the field also generally decreases as it is measured with increasing lateral displacement from the center line. An RF field that maintains relatively high intensity is said to be more “sensitive” in that it can sense the presence of an RFID circuit, such as on a tag borne by a participant, at a relatively greater distance from the antenna. A field that maintains intensity along the center line, but which drops off relatively quickly in intensity lateral to the center line is said to be “focused.”
The applicant's automated attendance monitoring system uses tags (worn or carried by students or other attendees) and readers to monitor the whereabouts of individuals. Thus, for instance, as students enter a classroom, the transceiver antenna of a reader placed near the door would interact with RFID circuits within the tags that are worn or carried by the students. The system would then track which students have entered the classroom, and by comparing the list of entering students with the class list, the system could generate a preliminary list of absent students (as well as present students). The teacher or other attendance monitor could then visually confirm attendance, and could use a handheld computer system to update and finalize the provisional attendance record.
In order for such an automated attendance tracking system to reliably monitor attendance, there must be constant, high quality communication between the tag and the antenna (also called the “transceiver”) of the reader. A number of factors can affect the ability of the tag to communicate with the antenna of the reader.
First, the position of the tag relative to the antenna of the reader can affect “readability.” Given current RFID technology, the tag should generally be parallel to the reader's antenna. For tracking the movement of inanimate objects, like inventory or crates, it is not difficult to maintain the tag in the proper orientation, but for humans, especially constantly moving students or employees, it is more difficult to maintain proper orientation.
Second, the signal emitted from the antenna of the reader maintains functional sensitivity in a somewhat conical shape RF field starting with a small cross-section (perpendicular to the center line extending from the antenna) close to the antenna and getting larger as the RF field extends farther away from the antenna. Because of this conical shape, tags that should not be read can be read, even though the tags are in locations where tag reading is not desired. For instance, students outside of a classroom and walking past a door to the classroom might have their tags read even though they never pass through the door. This problem exists in many applications of RFID equipment in other industries. Technicians are continually looking for ways to shield areas from the RF emitted from RFID equipment, so as to not read tags in certain locations.
Metal is commonly used as RF fields generally do not penetrate metal. Metal, however, has limitations, such as an undesirable ability to reflect RF electromagnetic radiation and can cause problems with ghosting of tags, and attenuating the strength of the RF field. This can cause non-reading of tags and lower the performance and reliability of the equipment. Known prior art RF absorption material has been found to be inadequate, as it did not control the location or focus of the RF field to a desired location. RF absorption materials also attenuate the RF signal significantly, so that maintaining accurate tag reads is made more difficult. Other RF shielding materials are commonly used to protect electronic equipment from interference. This invention is used to focus the RF field into a desired location without attenuating the strength of the RF signal or sacrificing any other performance characteristics.